Shigellosis is a global human health problem and a biodefense area of concern. The disease, caused by Shigella species, is a significant cause of morbidity and mortality accounting for 164 million cases worldwide and 1.1 million deaths annually, most notably amongst children. The disease is extremely infectious, requiring only 10-100 bacterial cells to initiate infection. Moreover, there is a global rise in the occurrence of multi-drug resistant isolates, such as the epidemic and pandemic Shigella dysenteriae type 1 strain. Despite this trend, the standard methods for the confirmed identification of the disease and the determination of antibiotic susceptibility, are traditional culturing methods, followed by serological and biochemical tests; these assays require 24-48 h to complete in a lab environment. The long-term goal of this research is to develop a rapid, and portable diagnostic assay technology that can detect the causative agents of shigellosis. Importantly, the diagnostic technology will be able to simultaneously provide an antibiotic susceptibility profile, which will enable appropriate treatment options and thus lead to improved patient prognosis. The R21 phase will generate the proof-of-principle results for the development of light-tagged Shigella reporter phages that can detect Shigella spp. by specifically conferring a bioluminescent signal response. Aim 1 will identify and prioritize Shigella phages which display species specificity and broad strain infectivity. Aim 2 will integrate the bacterial luxAB reporter genes into non-essential sites of the prioritized Shigella phage genomes to create luxAB-tagged reporter phages. In the presence of target bacteria, the reporter phage bind to specific cell receptors, inject their phage DNA, and use the hosts transcriptional and translational machinery to produce the luciferase enzyme. Upon substrate addition, the ensuing bioluminescent response can be readily detected. Following the demonstration that the Shigella reporter phages have the necessary detection attributes, the R33 grant will develop the reporter phage technology into a clinical diagnostic for shigellosis. We hypothesize that the bioluminescent phage detection system will be able to: (i) rapidly (within minutes) detect the presence of Shigella and differentiate between the species; (ii) require significantly fewer cells to achieve a positive signal (more sensitive); (iii) function directly with clinical specimens (does not require the isolation of pure bacterial cultures); (iv) provide concurrent antibiotic susceptibility data (and help patient prognosis), and (v) function with a simple handheld detection device (field appropriate/battery operated system). The cost of producing the reporter phage and the consumable costs are minimal. The assay does not require technical expertise or processing. Consequently, we believe the technology is particularly well suited to resource-limited settings and will be able to function in a non-laboratory environment as per the requirements set forth in this RFA.